The present disclosure relates generally to a method for providing an anti-stiction coating on a metal surface.
Stiction may occur in microelectromechanical systems (MEMS) in two different forms: between the substrate and the microstructure(s) and/or between two or more microstructures when the system is in operation. Anti-stiction coatings have been added to various surfaces in MEMS devices in an effort to prevent stiction from occurring.
Some anti-stiction coatings suitable for metal surfaces of a MEMS device include perfluorooctanoic acid (PFOA) or perfluorodecanoic acid (PFDA). While these materials are relatively compatible with the metal surfaces, they are often used at high excess levels to ensure protection of the surfaces. Furthermore, these materials may exhibit durability and volatility issues. Reduced durability of such anti-stiction coatings may result from the relatively weak bonds that are formed between the coating and the metal surface. A reduction of the contact angle when the material (e.g., PFOA on a TaAl surface) is exposed to heat indicates that the material is volatizing.
Furthermore, the reaction of some anti-stiction coatings (e.g., fluorinated decyl trichloro silane (FDTS) and/or other like materials) with metal surfaces may result in the formation of undesirable corrosive species (e.g., hydrochloric acid). Such species may attack the metal surfaces, thereby reducing reflectance and roughening the surface.